Currently the oldest known writing system in all of Central and South America dates to about 400 B.C. and is from cultures based in what is now Oaxaca, Mexico.

But William Saturno, the lead researcher reporting the find, points out that this "largely depends on what your definition of writing isthat is, the very first symbols, the first calendric signs, the first full-blown text, et cetera."

Saturno, an assistant professor of anthropology at the University of New Hampshire, and colleagues describe the Maya hieroglyphs in today's Science Express, the online advance version of the research journal Science. Their research at the San Bartolo site is partially funded by the National Geographic Society.

"The story of script invention in Mesoamerica is likely to get more and more complicated in the near future as more early texts from excavations in the Maya area come to light," Saturno said.

An Unusual Find

The ruins, which were discovered in 2001, consist of several buildings constructed at different times. In April 2005 Saturno was working in one part of the site while his colleague Boris Beltrán, of the University of San Carlos in Guatemala, worked in another, older section of the excavation.

"We're in a room built around 100 B.C. working on some murals," Saturno recalled, "and Boris was in a tunnel far deeper in the pyramid, going back further in timeabout four construction phases earlier than where the murals are."

Beltrán was working on defining the shapes and dimensions of the entire structure so he could see how the complex grew over time.

"One day Boris turns up some painting," Saturno said, "and he says, You should come back here. And I thought, Yeah, sure Borisit had become a running joke, because we kept finding fragments of mural everywhere."

"So I walked back into this tunnel, climbed the stairway on the back side of the building he's been excavating, and I look. And he's there with a big block with a painting of the [Maya] maize god on it [from] a couple of hundred years earlier than what we've been looking at.